If eligible to participate in the research study after completing the physical screening procedures, participants will be asked to return to the Substrate Metabolism Laboratory on another occasion after a short fast (no food or beverages - besides water) for at least 6 hours. After participants arrive, participants will rest quietly for approximately 30 min. The investigators will then collect a blood sample from a vein in participants hand, or forearm. After obtaining a baseline blood sample, participants will exercise at a moderate intensity (on a treadmill or a stationary bike) for one hour. This one hour moderate exercise session will feel like a slow jog during which participants would be able to carry a conversation. In order for the investigators to measure energy expended and the amount of fat participants are burning during exercise, the investigators will periodically ask participants to breathe through a mouthpiece so the investigators can collect participants expired breath. After the exercise session the investigators will collect another blood sample from a vein in participants hand, or forearm.